The invention relates to a process for the solvent extraction of solid carbon-containing materials, principally coal at elevated temperatures and at pressures which are above the vapor pressure of the solvent at the temperature employed. Specifically, the process relates to such processes which are carried out without catalysts. The invention also includes an apparatus for carrying out the process.
In this kind of process one tries to obtain from the unrefined raw material as high a percentage as possible of the desired useful components. The extraction of only a certain part of the raw material can also be of interest for the improvement of its technological properties for use in further refining processes. The extraction or part extraction involves also the problem of the removal of the undissolved residual solids from the solvent-extract mixture. The technological and economical usefulness of a particular process accordingly is determined by the combination of these two steps, that is extraction and elimination or removal of the extracted solids. A special object is in general to carry out the extraction in a continuous process which would result in substantial economical advantages.
From the German Pat. No. 663,497 it is known that coal extracts can be obtained from all kinds of coal by carrying out the extraction in a stage slightly above the decomposition stage of the insoluble residual coal which forms eventually in the step-by-step extraction at increasing temperatures (German Pat. No. 632,631). In an example of the first-mentioned patent a dried long-flame gas coal is extracted in 165 minutes at up to 63%. It is, however, noted there that by substantially departing from the stated temperature, either upwards or downwards, the extract yield is reduced.
If higher extract yields are to be obtained, it is necessary according to the just-mentioned German Pat. No. 612,631, to effect the extraction at temperatures below the decomposition temperature of the coal used as starting materials or any remaining residual material. In this process the temperature is increased step-by-step and the residual coal is separated from the solvent after each stage. Thus, each stage may have its own process cycle.
A shortcoming of these processes is, apart from the economically usually still unsatisfactory degree of decomposition, the large amount of time of at least 150 minutes which is necessary for such extraction and it is furthermore necessary in these processes to effect the separation of the residual solids from the solvent-extract mixture affer completion of the extraction. The latter step has been found to be exceedingly difficult, particularly in case of highly viscous extract components. These problems of the extraction process are also mentioned in the published German applications Nos. 2,522,772 and 2,522,746.
It is therefore an object of the present invention to make possible the complete decomposition of the solid carbonaceous material, and this without addition of a catalyst, only by means of conventional solvents. The process is to be carried out in a continuous or semicontinuous operation and without external separation problems between the residual coal and the extract-charged solvent. Besides, the time necessary for the total process is to be substantially reduced compared with the prior art processes. In addition the invention has the object of permitting a quick pretreatment of solid carbon-containing materials in order to modify their technological properties.